The recommendation for initial topical therapy applies to the otherwise healthy patient with diffuse AOE that is not complicated by osteitis, abscess formation, middle ear disease, or recurrent episodes of infection. Topical therapy should be supplemented by systemic antibiotics if the affected individual has a condition, especially diabetes that is associated with markedly increased morbidity, or HIV infection/ AIDS or other conditions with immune deficiency that could impair host defenses; if the infection has spread beyond the confines of the ear canal into the pinna, skin of the neck or face, or into deeper tissues such as occurs with malignant/necrotizing external otitis; or if there is good reason to believe that topical therapy cannot be delivered effectively (see section 6, application) (Rowlands 2001, Zikk 1991). There is no trial to evaluate the efficacy of cleaning of the ear canal, whereas cleaning and placebo drops only achieves a cure rate of 10% (Kaushik 2010).

Topical preparations are recommended as initial therapy for diffuse, uncomplicated AOE because of safety, efficacy over placebo in randomized trials, and excellent clinical and bacteriologic outcomes in comparative studies. There are no data on the efficacy of systemic therapy alone with the use of appropriate antibacterials and stratified by severity of the infection. Moreover, orally administered antibiotics have significant adverse effects that include rashes, vomiting, diarrhea, allergic reactions, altered nasopharyngeal flora, and development of bacterial resistance (Doern 2000, McCormick 2003, Schrag 2004, Pottumarthy 2005). Societal consequences include direct transmission of resistant bacterial pathogens in homes and child care centers (Levy 2002).

Topical antimicrobial treatment vs placebo

Three randomized trials have compared topical antimicrobial vs placebo for treating diffuse AOE (Cannon 1967, Cannon 1970, Freedman 1978). Meta-analysis of the 2 trials with similar methods (Cannon 1967, Cannon 1970) yields a combined absolute rate difference (RD) of 0.46 based on 89 patients (95% CI, 0.28 to 0.63), which suggests that only 2 patients needed to be treated (NNT) with topical antimicrobial to achieve 1 additional cure. Bacteriologic efficacy (RD, 0.61) was higher than clinical efficacy. Another trial (Freedman 1978) reported significantly less edema and itching 3 days after therapy was initiated, and less edema, itching, redness, scaling, and weeping 7 days after therapy was initiated.

Topical vs systemic antibiotics

No randomized, controlled trials have directly compared oral antibiotic therapy alone, with topical therapy. Reviews of survey data, however, show that about 20% to 40% of subjects with AOE receive oral antibiotics, often in addition to topical antimicrobials (Rowlands 2001, Halpern 1999, McCoy 2004). Many of the oral antibiotics selected are inactive against P aeruginosa and S aureus, the most common pathogens identified in cases of AOE. Further, treatment with penicillins, macrolides, or cephalosporins increases disease persistence (rate ratios, 1.56 to 1.91), and treatment with cephalosporins also increases recurrence (rate ratio, 1.28; 95% CI, 1.03 to 1.58) (Rowlands 2001).

Topical + systemic antibiotics vs topical antimicrobial + placebo

One study is comparing oral antibiotics (amoxicillin) and topical (non-quinolone) antibiotic/ steroid drops with topical (quinolone)/ steroid drops (Roland 2008), and found no difference between groups. In an additional study (Yelland 1993) patients were randomized to topical ointment plus oral antibiotic (trimethoprim-sulfamethoxazole) vs topical ointment plus placebo; there was no significant difference in cure rates at 2 to 4 days (RD, – 0.01; 95% CI, – 0.21 to 0.18) or at 5 to 6 days (RD 0.08; 95% CI, – 0.15 to 0.30).

Resistance and Therapeutic concentration

An advantage of topical therapy is the very high concentration of antimicrobial that can be delivered to infected tissue, often 100 to 1000 times higher than can be achieved with systemic therapy. For example a 0.3% solution of antibiotic (a typical concentration in commercial otic drops) has a concentration of 3000 mcg/mL. Any organisms known to cause AOE, even those considered “resistant,” will be unlikely to survive contact with this antibiotic concentration. Because there are between 10 to 20 drops/mL, depending on the nature of the liquid (solution vs suspension, viscosity, etc), each dose of 3 to 5 drops contains about 0.5 to 1.5 mg of antibiotic.

Topical therapy avoids prolonged exposure of bacteria to subtherapeutic concentrations of antibiotic, and may therefore be less likely than systemic therapy to result in selective pressure for resistant organisms (Roland 2002, Weber 2004). The avoidance of antibiotic exposure of host bacteria resident outside the ear canal, as occurs with systemic therapy, provides a further advantage to the reduction of the selection of resistant microorganisms. Restrictive use of oral antibiotics for AOE is important because of the increased resistance among common AOE pathogens, especially S aureus and P aeruginosa (Walshe 2001, Cantrell 2004).

Topical treatment without antibiotics

Effective topical treatments include acetic acid (Balen van 1993, Cannon 1970, Kime 1978, Ordonez 1978), boric acid (Slack 1978),aluminum acetate (Clayton 1990, Lamber 1981), silver nitrate (Smathers 1977, Hasselt van 2004), and an endogenous antiseptic N-chlorotaurine (Neher 2004). Topical steroids are also effective, as a single agent (Ruth 1990, Tsikoudas 2002, Emgard 2005), or in combination with acetic acid (Balen van 1993, Kime 1978, Ordonez 1978) or an antifungal preparation (Bak 1983). When the success of these nonantibiotic therapies is considered, it is likely that for cases of uncomplicated AOE, oral antibiotics, particularly those with no activity against P aeruginosa or S aureus, are unnecessary. From the Cochrane review becomes apparent that most topical treatments are equally effective (Kaushik 2010).

Lifestyle recommendations during treatment

Along with prescribing topical antimicrobials, clinicians should advise patients to resist manipulation to minimize ear trauma and should discuss issues that pertain to water restrictions during treatment. The insertion of earplugs or cotton (with petroleum jelly) before showering or swimming can reduce the introduction of moisture into the ear. The external auditory canal can be dried after swimming or bathing with a hair dryer on the lowest setting. Patients with hearing aids or ear phones should limit insertion until pain and discharge (if present) have subsided.